# All Questions

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### Avoiding doubled letters in encrypted text

I have an encrypted string based on an "alphabet" of 29 runes and access to successfully decrypted (runes->English) plaintext. Testing for a Vigenere cipher, I tried a Friedman attack (aka Kappa test, ...
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### Why is a LCG not suitable for use in a cryptographic primitive?

Two's complement addition (and multiplication) are non-linear with respect to XOR and AND. This means that for bit vectors over $\mathbb{Z}_2$, the operation $a + x$ cannot be expressed as the matrix ...
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### How do they avoid Zero Knowledge Proofs in the paper Priced Oblivious Transfer: How to sell Digital Goods?

I don't understand a part of the paper Priced Oblivious Transfer - How to Sell Digital Goods. Particularly, the authors avoid using zero knowledge proofs and in section 3.3 they explain how they do ...
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### Proof of IND-q-CCA security

I have some questions about the paper Bounded CCA2-Secure Encryption (pdf). On page eight "3.2 Construction", the authors have done a black-box construction of an IND-q-CCA security schema and then ...
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### how to verify subset of hashes from hash list

I need to verify a couple hashed (SHA256) integers from a list of approximately 50 hashed integers in a message. The list can be divided into groups. The (plain) integer data is not in the message, ...
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### Password hashing in embedded systems

Are there good options for password hashing in embedded systems? These systems often cannot afford slow has functions. I can think of a few approaches: Store the (hashed) passwords in a HSM that ...
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### Is it safe to use a key as message in keyed hashing (HMAC)?

Scenario: User gives password. A "password key" is derived from the password (e.g. by PBKDF2). A random salt is applied. The password key is hashed with a HMAC algorithm (e.g. HMAC-SHA256), with ...
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### Active s-box of 8x8 MDS for AES

one way to enhance the security of AES by increasing the number of active s-boxes .larger MDS matrices are used to increase the number of active s-boxes. using 4x4 MDS matrix generate 25 active s-box ...
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### Are there unreachable MD5 hashes? [duplicate]

Are there any known MD5 hashes that can´t occure, no matter what (finite) input is taken? Thanks
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In the Mac-forge experiment, the adversary is given access to a tag-generation oracle, which generates a tag for each message given by the adversary. The adversary's task is to generate a valid tag on ...
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### Why is AES-128 considered secure while RSA needs a 1024-bit size to be considered secure [duplicate]

I got asked this question today and I didn't know the answer, AES-128 is considered secure, the key size is 2^128, so you would need in average 2^127 tries to break the key. Why does RSA need at least ...
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### Gaussian distribution in lattices

In many lattice based cryptosystems, Gaussian distribution is used. Can you explain why only Gaussian distribution is preferred?
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### Compression in key generation of DES algorithm

Does anyone have a pseudo-code or an algorithm or even a diagram of the compression (pc2) of the DES algorithm? I can't find a relation between the bits that are dropped, even when I do it manually ...
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### Construction of division polynomials

I'm trying to understand the construction of the division polynomials used in Schoof's algorithm. I firstly followed this report of Charlap and Robbins. I stuck with the definition of the leading ...
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### Are collisions in AES-128 theoretically possible when the plaintext is the same? [duplicate]

Is it theoretically possible to find $P$, $K$, and $K^\prime$ such that $E_K(P) = E_{K^\prime}(P)$ where $E$ is AES-128 and $K \ne K^\prime$? I'd imagine this would be infeasible, but is it actually ...
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### Q: Relevance of physical layer security to cryptography

I found that there are quite some active research activities in a field named "physical layer security", with in particular some types of codes that apparently are different from those commonly ...
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### System parameters in identity-based encryption

In IBE schemes, the system parameters are $(q, \mathbb{G}, F, \hat{e}, P, Q, T, H_1)$. I don't know $\hat{e}$. For example, in type A pairing… ...
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### Using e-ID Number for Encryption and Digital Signing

I want to use e-ID number for performing Encryption/Decryption and Digital Signing - and in order to do so, I've opted a PGP-oriented approach which goes a bit like this. Generating PGP key-pair ...
Given the affine form of coordinates $(x,y)$ such as $(5,3)$, if I want to convert $(5,3)$ to projective coordinates $(x,y,z)$, should the form of point be $(5,3,1)$? It is triplet not a point, right? ...
I am working with my project. I use projective coordinates but when I convert to affine coordinates, I can't get it. Can anyone help me? Projective Coordinates $(X,Y,Z)$ to Affine Coordinates $(X,Y)$:...